A number of postprandial endocrine, paracrine or autocrine messenger products involved in the signaling of hunger and satiety that are present in circulation such as hormones or peptides. The results from an elevated or reduced plasma concentration of one or more of these products will have either global orexigenic or anorexigenic effects.
Examples of peptides associated with anorexigenic effects are pancreatic polypeptide (PP), neuropeptide Y (NPY) and peptide YY (PYY).
These peptides act through Y receptors for which five are known, Y1, Y2, Y3, Y4 and Y5 and regulate pancreatic secretion, gastric emptying and gastric motility. The Y receptors are found throughout the peripheral and central nervous systems as well as on various gastrointestinal organ cells.
Pancreatic polypeptide is secreted in the pancreas and helps control energy homeostasis through inhibition of pancreatic secretions such as for example insulin thus leading to an increased blood glucose level and signaling a need for reduced feeding.
Hypothalamic secreted neuropeptide Y participates in the control of food intake through binding and activation Y1 and possibly Y2 and Y5 receptors.
One of the most discussed examples in recent times is PYY1-36. It is produced in endocrine L cells lining the distal small bowel and colon. The prepro PYY is clipped by signal peptidases to give proPYY1-70. This peptide is further modified by prohormone dibasic convertase leading to PYY-Gly-Lys-Arg followed by Carboxypeptidase B to give PYY-Gly and finally to PYY1-36 by amidation enzyme. It is then released from the cell where a metabolic derivative obtained through DPP-IV cleavage of the two N-terminal amino acids give circulating PYY3-36.
PYY1-36 binds and activates Y1, Y2 and Y5 receptors found on a variety of cells surfaces as for NPY. The cells are found peripherally in the gastrointestinal tract as well as on the arcuate nucleus. The result of interaction with the Y2 found on the arcuate is thought to lead to a central nervous system response. Alternatively the Y2 receptors found peripherally on the surface of cell within the gastrointestinal tract have been shown to have an effect on gastric motility, gastric acid secretion and intestinal motility. The result of these interactions lead to reduced food and caloric intake.
Unlike PYY1-36 which interacts equally with the Y1 and Y2 receptors, PYY3-36 is selective to the Y2 receptor. A selective agonist of the Y2 receptor has been demonstrated to be beneficial as compared to a broad agonist. In fact, the Y1 receptor has been associated with hypertension (A. Balasubramaniam et al. J. Med. Chem. 2000, 43, 3420-27, Balasubramaniam A et al. Pept Res. 1988 1, 32-5). PYY3-36 has been demonstrated to reduce food intake in vivo (Nature, 2002, 418, 650-4).
The advantage of using PYY3-36 is that it is a natural appetite controlling hormone. There will not psychological side effect from the central nervous system such as when norepinephrine and serotonin reuptake inhibitor or other stimulants are used. Another advantage is that this class of therapeutic agent does not interfere with the absorption of certain nutritional or fat containing elements such as gastrointestinal lipase inhibitor that cause uncomfortable side effects. An inconvenience of using PYY3-36 is need for multiple daily administrations.
A new anti-obesity agent that has an enhanced activity and which would permit to avoid the above-mentioned drawbacks would therefore be highly desired. A method for enhancing the anti-obesity activity of a PYY peptide or a functional derivative thereof would also be desired.